Mary stopped work at 5:15 this afternoon. She had worked eight hours and 25 minutes. When did she begin working today?

Answer 1

Since Mary ended her work day at 5:15pm and she worked 8 hours and 25 minutes

First, go back 8 hours from 5:15pm,

This will give you 9:15am

Second, take 25 minutes from 9:15am,

This will give you 8:50am

So Mary started her work day at 8:50am

Answer 2

If you were using a 24-hour clock, 5:15 pm would be 5:15 + 12 = 17:15 hours.

Take away 8 hours - that's 9:15 hrs. Now we need to subtract another 25 minutes.

Minus 15 minutes brings us to 9 hours; another 10 minutes is 8:50 am, when she started working.